[feature] Add rate limit exceptions option, use ISO8601 for rate limit reset (#2151)

* start updating rate limiting, add exceptions

* tests, comments, tidying up

* add rate limiting exceptions to example config

* envparsing

* nolint

* apply kimbediff

* add examples

internal/middleware/ratelimit_test.go

@@ -0,0 +1,192 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package middleware_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
+	"github.com/superseriousbusiness/gotosocial/internal/util"
+)
+
+type RateLimitTestSuite struct {
+	suite.Suite
+}
+
+func (suite *RateLimitTestSuite) TestRateLimit() {
+	// Suppress warnings about debug mode.
+	gin.SetMode(gin.ReleaseMode)
+
+	const (
+		trustedPlatform = "X-Test-IP"
+		rlLimit         = "X-RateLimit-Limit"
+		rlRemaining     = "X-RateLimit-Remaining"
+		rlReset         = "X-RateLimit-Reset"
+	)
+
+	type rlTest struct {
+		limit        int
+		exceptions   []string
+		clientIP     string
+		shouldPanic  bool
+		shouldExcept bool
+	}
+
+	for _, test := range []rlTest{
+		{
+			limit:        10,
+			exceptions:   []string{},
+			clientIP:     "192.0.2.0",
+			shouldPanic:  false,
+			shouldExcept: false,
+		},
+		{
+			limit:        10,
+			exceptions:   []string{},
+			clientIP:     "192.0.2.0",
+			shouldPanic:  false,
+			shouldExcept: false,
+		},
+		{
+			limit:        10,
+			exceptions:   []string{"192.0.2.0/24"},
+			clientIP:     "192.0.2.0",
+			shouldPanic:  false,
+			shouldExcept: true,
+		},
+		{
+			limit:        10,
+			exceptions:   []string{"192.0.2.0/32"},
+			clientIP:     "192.0.2.1",
+			shouldPanic:  false,
+			shouldExcept: false,
+		},
+		{
+			limit:        10,
+			exceptions:   []string{"Ceci n'est pas une CIDR"},
+			clientIP:     "192.0.2.0",
+			shouldPanic:  true,
+			shouldExcept: false,
+		},
+	} {
+		if test.shouldPanic {
+			// Try to trigger panic.
+			suite.Panics(func() {
+				_ = middleware.RateLimit(
+					test.limit,
+					test.exceptions,
+				)
+			})
+			continue
+		}
+
+		rlMiddleware := middleware.RateLimit(
+			test.limit,
+			test.exceptions,
+		)
+
+		// Approximate time when this limiter will reset.
+		resetAt := time.Now().Add(5 * time.Minute)
+
+		// Make requests up to +
+		// just over the limit.
+		limitedAt := test.limit + 1
+		for requestsCount := 1; requestsCount < limitedAt; requestsCount++ {
+			var (
+				recorder = httptest.NewRecorder()
+				ctx, e   = gin.CreateTestContext(recorder)
+			)
+
+			// Instruct engine to derive
+			// clientIP from test header.
+			e.TrustedPlatform = trustedPlatform
+			ctx.Request = httptest.NewRequest(http.MethodGet, "/example", nil)
+			ctx.Request.Header.Add(trustedPlatform, test.clientIP)
+
+			// Call the rate limiter.
+			rlMiddleware(ctx)
+
+			// Fetch RL headers if present.
+			var (
+				limitStr     = recorder.Header().Get(rlLimit)
+				remainingStr = recorder.Header().Get(rlRemaining)
+				resetStr     = recorder.Header().Get(rlReset)
+			)
+
+			if test.shouldExcept {
+				// Request should be allowed through,
+				// no rate-limit headers should be written.
+				suite.Equal(http.StatusOK, recorder.Code)
+				suite.Empty(limitStr)
+				suite.Empty(remainingStr)
+				suite.Empty(resetStr)
+				continue
+			}
+
+			suite.Equal(strconv.Itoa(test.limit), limitStr)
+			suite.Equal(strconv.Itoa(test.limit-requestsCount), remainingStr)
+
+			// Ensure reset is ISO8601, and resets at
+			// approximate reset time (+/- 10 seconds).
+			reset, err := util.ParseISO8601(resetStr)
+			if err != nil {
+				suite.FailNow("", "couldn't parse %s as ISO8601: %q", resetStr, err.Error())
+			}
+			suite.WithinDuration(resetAt, reset, 10*time.Second)
+
+			if requestsCount < limitedAt {
+				// Request should be allowed through.
+				suite.Equal(http.StatusOK, recorder.Code)
+				continue
+			}
+
+			// Request should be denied.
+			suite.Equal(http.StatusTooManyRequests, recorder.Code)
+
+			// Make a final request with an unrelated IP to
+			// ensure it's only the one IP being limited.
+			var (
+				unrelatedRecorder        = httptest.NewRecorder()
+				unrelatedCtx, unrelatedE = gin.CreateTestContext(unrelatedRecorder)
+			)
+
+			// Instruct engine to derive
+			// clientIP from test header.
+			unrelatedE.TrustedPlatform = trustedPlatform
+			unrelatedCtx.Request = httptest.NewRequest(http.MethodGet, "/example", nil)
+			unrelatedCtx.Request.Header.Add(trustedPlatform, "192.0.2.255")
+
+			// Call the rate limiter.
+			rlMiddleware(unrelatedCtx)
+
+			// Request should be allowed through.
+			suite.Equal(http.StatusOK, unrelatedRecorder.Code)
+
+		}
+	}
+}
+
+func TestRateLimitTestSuite(t *testing.T) {
+	suite.Run(t, new(RateLimitTestSuite))
+}